Papermaking process comprising the incorporation of a polyacrylamide mucilaginous material

ABSTRACT

A PROCESS IS PROVIDED FOR THE PREPARATION OF CELLULOSIC PAPER SHEETS HAVING A HIGH DEGREE OF UNIFORMITY. IN THIS PROCESS, AN IMPROVEMENT HAS BEEN DISCOVERED WHICH COMPRISES (1) SEQUESTERING THE EXCESS ALUMINUM ION BY THE ADDITION OF A SEQUESTERING AMOUNT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF (I) A CHELATING AGENT AND (II) AN ACRYLAMIDE-BASED ANIONIC POLYMER HAVING A MOLECULAR WEIGHT OF LESS THAN 1,000,000, AND (2) AFTER SEQUESTERING THE EXCESS FREE ALUMINUM ION, THEN INCLUDING IN SAID FIBER SUSPENSION 0.01-2% (BASED ON DRY FIBER WEIGHT) OF A POLYACRYLAMIDE MUCILAGINOUS MATERIAL OF A MOLECULAR WEIGHT OF MORE THAN 3,000,000 AND A HYDROLYSIS DEGREE OF 10 TO 30%. THE PROCESS ALLOWS THE FORMATION OF PAPER SHEETS OF AN EVEN TEXTURE AND QUALITY BY OBVIATING THE PROBLEM OF CELLULOSE FIBER SLIPPAGE ON THE WIRE MESH AND PROVIDES A UNIFORM DISPERSION OF THE FIBERS IN THE VAT.

United States Patent 3,725,195 PAPERMAKING PROCESS COMPRISING THE INCORPORATION OF A POLYACRYLAMIDE MUCILAGINOUS MATERIAL Fujio Suyama and Tokuo Yamamoto, Shizuoka, Kenicln Shimono and Hirosi Kuwahara, Fuji, Masao Ishu, Tokyo, and Ichiro Watanabe, Yokohama, Japan, assignors to Nitto Chemical Industry Co., Ltd., and Shizuoka-ken, Shizuoka-shi, Japan No Drawing. Filed Aug. 10, 1970, Ser. No. 62,703 Claims priority, application Japan, Aug. 11, 1969,

44/62,932; Oct. 31, 1969, 44/86,852; Nov. 12, 1969, 44/ 90,007

Int. Cl. D21h 3/58 US. Cl. 162-168 6 Claims ABSTRACT OF THE DISCLOSURE A process is provided for the preparation of cellulosic paper sheets having a high degree of uniformity. In this process, an improvement has been discovered which comprises 1) sequestering the excess aluminum ion by the addition of a sequestering amount of a member selected from the group consisting of (i) a chelating agent and (ii) an acrylamide-based anionic polymer having a molecular weight of less than 1,000,000; and (2) after sequestering the excess free aluminum ion, then including in said fiber suspension 0.01-2% (based on dry fiber weight) of a polyacrylamide mucilaginous material of a molecular weight of more than 3,000,000 and a hydrolysis degree of 10 to 30%. The process allows the formation of paper sheets of an even texture and quality by obviating the problem of cellulose fiber slippage on the wire mesh and provides a uniform dispersion of the fibers in the vat.

This invention relates to a process for manufacturing paper by use of a synthetic mucilaginous material. Research efforts have been conducted on papermaking by use of a synthetic mucilaginous material for fiber dispersion, anti-freeness and anti-sedimentation, in order to improve uniformity of the paper produced as well as to ensure smooth operation of sheetmaking in manufacturing paper by a paper machine.

For instance, there is found a case where a comparatively low molecular weight water-soluble polyelectrolyte with a strongly anionic property was used. However, when such a polymer is used as a synthetic mucilaginous material, the cellulose fiber is apt to slip down along the surface of cylinder wire, a phenomenon called Washotf, resulting in poor wet web formation so that a continuous operation of manufacturing paper of sutficient commercial value becomes impossible. Moreover, because of a strong adhesiveness said water-soluble polyelectrolyte tends to adhere to the dryer surface of a paper machine, causing frequent broke which renders a continuous operation of papermaking difiicult.

On the other hand, although developmental research had been done in the past on making use of polyphosphates, carboxymethylcellulose, sodium alginate and the like as a synthetic mucilaginous material, satisfactory effects of dispersion, anti-freeness and anti-sedimentation on fiber were unattainable and these compounds are currently not in use.

It was only recently that the research on utilization of the polyethylene oxide (hereinafter referred to simply as PEO) as a synthetic mucilaginous material made progress, and this compound is gradually coming into use. However, when said compound was used there arose new difficulties such as a decrease in papermaking speed due to foaming of the stock, necessity of adding an antifoaming agent, a decrease in the sizing effect and in the strength of paper, resulting from said addition of an antifoaming agent, and development of unevenness in color which is caused by aggregation of fibers in the paper made from the stock containing dyes. Therefore, development of a novel synthetic mucilaginous material has been desired.

The sheet formation on a cylinder machine takes place as follows: the fiber suspension in a cylinder vat is subjected to suction at the surface of a cylinder wire, and forms wet web on the surface of cylinder as the cylinder rotates. When a synthetic mucilaginous material with insufiicient effects of dispersion, anti-freeness and antisedimentation on fiber is used, the cellulose fiber tends to slip down along the surface of cylinder wire, a phenomenon called wash-off; this results in a poor sheet formation leading to appearance of a strip-pattern in the final paper owing to the differences in thickness between a thick part and a thin part. Further, the synthetic mucilaginous material having excellent effects of dispersion, anti-freeness and anti-sedimentation on fiber is not only necessary for a cylinder machine but also, of course, desirable to be used for a Fourdrinier machine to obtain a satisfactory formation of uniform wet web.

The Wash-off can be avoided by suppressing to a certain extent the freeness of the cellulose fiber. As one of the means to judge the degree of suppression of the freeness,

there is a method which consists in comparing the difference in liquid levels inside and outside the cylinder. Generally, it is recognized that as said difference becomes greater the Wash-off tends to disappear.

The present inventors evaluated various substances as a synthetic mucilaginous material for paperma-king by adopting the following procedure as a means to show quantitatively the good or bad sheet formation: The thickness of the final paper was measured at several points situated at regular intervals along the cross-direction of the final paper, and the mean value of these measurements was determined at regular intervals along the machine direction of the paper; from a series of these mean values, the difference in thickness between the thick part and the thin part of the paper was obtained, and this difference served as the basis for the evaluation. As a result, it was found that a polyacrylamide having both of the specific molecular weight and specific hydrolysis degree has a pronounced ability for wet web formation and gives a good result. Based on this finding, the present invention has been accomplished.

The polyacrylamide to be used in this invention should have a hydrolysis degree within the range of 10 to 30%. When a polyacrylamide having a hydrolysis degree of less than 10% is used, the uniformity of the formed sheet tends to become worse; however when the hydrolysis degree exceeds 30% a sticking tendency onto the dryer surface becomes noticeable and dry broke is induced.

Said efiect according to the degree of hydrolysis is considered to be due to the influence of the hydrogen bond of the carboxylic group. For example, in the case where the number of carboxylic groups is too small, the number of hydrogen bonds is also small, and it becomes difficult to maintain a uniform state of felting of cellulose fibers produced by the synthetic mucilaginous material, while in the case where the number of carboxylic groups is too large a good result is still obtained as for the sheet formation but a sticking tendency onto the dryer surface becomes stronger and more distinguished than said effect of uniform state of felting, and the sum total of the effects would be only negative.

The molecular weight of polyacrylamide used as a synthetic mucilaginous material in this invention is preferably larger than 3,000,000. When polyacrylamide having a molecular weight less than 3,000,000, for example, a molecular weight of about 2,500,000, is used, the uniformity of formed sheet often becomes inferior, however controlled the hydrolysis degree of the polymer may be. Although in this case the uniformity of formed sheet may sometimes be improved by the addition of an increased amount of the synthetic mucilaginous material, the addition of a large amount of synthetic mucilaginous material is undersirable from an economical point of View.

Though the amount of the synthetic mucilaginous material used in this invention can be decreased with the increase in the polymerization degree thereof, it is generally effective when present in an amount of 0.01% 'by weight or more based on the weight of dry fiber. From an economical and other points of view, the preferred amount is 2.0% by weight or less.

The partial hydrolyzate of polyacrylamide used as a synthetic mucilaginous material can be prepared by conventional methods. It may also be prepared by the following procedure:

An aqueous solution containing 3 to 20% by weight of acrylamide monomer is placed in a vessel provided with a reflux condenser; it is allowed to polymerize with stirring under a nitrogen stream using as catalyst 0.01 to 0.1% (based on the weight of monomer) of a persulfate or hydrogen peroxide, or using, if necessary, as a redox catalyst a combination of these compounds with 0.01 to 0.1 by weight of dimethylaminopropionitrile, triethanolamine, sodium thiosulfate, sodium sulfite, ferrous sulafte, or the like. The reaction is run at a temperature of to 50 C. for several to approximately ten hours to obtain an aqueous solution of polyacrylamide. Then, after adding 10 to 30% by mole of a caustic alkali per mole of the polyacrylamide, said solution is stirred at 50 to 90 C. for 2 to 3 hours, to yield a partial hydrolyzate of polyacrylamide having a molecular weight of 3,000,000 or more. The aqueous polymer solution thus obtained has a viscosity of within the range of 100,000 to 500,000 cps. at a concentration of 5%. In actual use, the solution is further diluted to a polymer concentration of 0.001 to 0.1%.

The synthetic mucilaginous material of the present invention cannot be used directly in a rosin-sized stock suspension, because if used, the fibers flocculate so badly that the sheet forming becomes impossible. This phenomenon seems to be caused by the following reasons: the decrease in viscosity due to transformation of the polymer chain of polyacrylamide into a thread-ball-like shape, which is caused by the combination of excess aluminum ion produced by hydrolysis of aluminum sulfate added to fix the rosin sizing agent, with anionic carboxylic groups in the polyacrylamide added as a synthetic mucilaginous material; and the occlusion of fibers in the molecules of the synthetic mucilaginous material when these molecules crimple into a thread-ball-like shape.

The present inventors conducted a research on suppressing the phenomenon of fiber flocculation caused by the aluminum ion existing in excess. As a result, it was found that the phenomenon of fiber flocculation can be suppressed and the present synthetic mucilaginous material can be utilized in forming the sheet from a rosinsized stock, when said synthetic mucilaginous material is used after the addition of a chelating agent capable of combining ionically with aluminum ion, thereby sequestering the excess free aluminum ion; or after sequestering the excess aluminum ion by the addition of a polymer of the anionic polyacrylamide type having a chain length insufficient to fully occlude fibers when the polymer chain transforms into a thread-'ball-like shape.

As said chelating agent for aluminum ion, there are oxalic, malonic, succinic, maleic, malic, tartaric and citric acids, disodium nitrilotriacetate, disodium ethlylenediaminetetracetate, disodium N-oxyethylethylenediaminetriacetate, disodium 1,2 diaminocyclohexanetetraacetate, sodium sulfosalicylate and sodium catechol-3,5-disulfo nate, etc.

Though the amount of said chelating agent depends upon the amount of excess free aluminum ion, the addi- 4 tion of 0.05 to 2 moles thereof per mole of aluminum sulfate is generally suflicient.

As a relatively low molecular weight polymer of the acrylamide-type, which also sequesters the excess aluminum ion, there is used an anionic polymer of the polyacrylamide-type having a molecular weight of less than 1,000,000 (hereinafter referred to as acrylamide-based low molecular polymer). This polymer is not necessarily limited to a polymer of acrylamide, but a part of acrylamide can be substituted by one or more monomers selected from the group of copolymerizable monomers consisting of (meth)acrylic acid salts, (meth)acrylic acid esters, acrylonitrile, and vinyl acetate. In this case the content of the monomer(s) capable of copolymerizing with acrylamide in the copolymer should be less than 5 0% by weight. When said content in a copolymer exceeds 50%, there occurs in the course of papermaking an undesirable sticking onto the surface of a dryer of paper machine.

Though the amount of said acrylamide-based low mo lecular polymer to be used varies according to the amount of aluminum sulfate used in sizing treatment and to its capacity for capturing the aluminum ion, it should be added in an amount of 1 to 10 moles per mole of aluminum sulfate.

The acrylamide-based low molecular polymer used in this invention can be prepared by any 'known method. It may also be prepared by, for example, the following method: An aqueous solution containing 10 to 25% by weight of the monomer is placed in a vessel provided with a reflux condenser, and allowed to polymerize with stirring while nitrogen is being blown ion, using as catalyst 0.05 to 10% by weight (based on the weight of monomer) of a persulfate or hydrogen peroxide, or using, if necessary, as redox catalyst a combination of these compounds with 0.05 to 10% by weight of dimethylaminopropionitrile, triethanolamine, sodium thiosulfate, sodium sulfite, ferrous sulfate, or the like, at a temperature of 20 to 70 C. for one to several hours to complete the polymerization and to obtain an aqueous solution of the polymer. Those polymers which contain no carboxylic group in the molecule are further heated with stirring after addition of a caustic alkali in an amount corresponding to 1 to 30% by mole, at 50 to C. for 1 to 3 hours to obtain a partial hydrolyzate of the polymer. The aqueous polymer solution thus obtained has a viscosity of within the range of to 20,000 centipoise (cps.), as measured by a Brookfield viscometer at a polymer concentration of 10%. In actual use, said solution is further diluted to a polymer concentration of 0.5 to 5%.

The above-mentioned chelating agent or acrylamidebased low molecular polymer, which serves to sequester the excess free aluminum ion in rosin-sized stock is added to the stock subsequent to the sizing treatment with a rosin sizing agent and aluminum sulfate, and then a polyacrylamide having a molecular weight of more than 3,000,000 and a hydrolysis degree of 10 to 30% is added thereto, whereupon the sheet formation can be started, thus leading to an extremely smooth operation of making even a rosin-sized paper.

By use of the present synthetic mucilaginous material, the uniformity of final paper is improved, the sheetforming proceeds smoothly, and because of lack of flocculation of fibers the unevenness in color, which is attributable to the flocculation of dyed fibers, is entirely prevented, whereas said unevenness in color is observed in the case where polyethylene oxide is used in a dyed stock.

The present invention is further illustrated hereunder with reference to examples. In the examples, the measurement of dispersion level was evaluated from the light transmittance at 660 ru by use of a photoelectric colorimeter. The testing of sizing degree was conducted according to the method of HS P 8122. The testing of water absorption degree was conducted in accordance with the method specified in I IS P 8141.

EXAMPLE 1 In a Hollander beater 40 kg. of a commercial NBKP (coniferous bleached kr-aft pulp) was heated at a consistency of 3% (by weight; the sambe shall apply hereinafter) for one hour to a Canadian freeness of 650 to 700 cc. Then the stock was diluted to a consistency of 0.1%, and sent to a cylinder vat where the diluted stock was admixed with an aqueous polyacrylamide solution which had previously been diluted to a concentration of 0.1%. From the stock was made a tissue paper of 16.0 g./m. basis weight. The results of tests conducted on the final paper thus prepared were summarized in Table 1. The paper machine used was a cylinder Yankee machine of the uniflow type, and the width of sheet-forming was 445 mm.

Among the results of tests shown in Table 1, the rating of sheet formation was obtained as follows: by means of a micrometer a set of thickness measurements was made at 5 points spaced at every 5 cm. interval in a line along the cross direction of the sheet, commencing at a point 12.25 to the left edge of the sheet; a number of these sets of measurements were done along the machine direction of the sheet at every 2.5 cm. interval; the mean values of thicknesses of each set were determined and the ditference between the maximum and the minimum mean values was taken as the criterion in the following manner: excellent for the diiierence of 1p. or less, good for 1.1 to 1.5a, fair for 1.6 to 2.0a, and poor for 2.1,0. or more. In the sheet marked poor in this evaluation method, there was observed by visual inspection also a stripe pattern so distinct that the sheet was of no com- 6 EXAMPLE 3 In a Niagara beater, 650 g. of a commercial NBKP was heated at a consistency of 3% for 30 minutes to a Canadian freeness of 690 cc. After completion of the beater treatment, the stock was admixed with 1.0% (100% basis; the same shall apply hereinafter) on the basis of dry fiber of a rosin sizing agent and 0.9% on the basis of dry fiber of aluminum sulfate (containing 18 molecules of water of crystallization; the same shall apply hereinafter), and thoroughly mixed with stirring. The pH of the stock thus treated was 4.5.

Subsequently, as given in Table 3, disodium nitrilotriacetate (NTA--2Na) was added to the stock as a chelating agent in an amount of 1 to 2 moles per mole of added aluminum sulfate, and the stock was diluted to a consistency of 0.1%. A definite quantity of said diluted stock was admixed with 2% on the basis of dry fiber of a high-molecular weight polyacrylamide having a molecular weight of 5,000,000 and a hydrolysis degree of 20%, which had been prepared in advance. The measurement of dispersion level of fibers was evaluated from the light transmittance at 660 mn by use of a photoelectric colorimeter. On the other hand, the results of visual inspection were shown along with the light transmittance in the table, where poor means distinct appearance of flocculation and good means no flocculation on adding the synthetic mucilaginous material.

mencial value.

TABLE 1 Freeness Polyacrylamide of the stock in vat ad- Amount mixed with Head diiIerused synthetic ence between Degree on dry mucilaginous inside and Machine Frequency Basis M01. wt. hydrolysis fiber material outside of speed of adherence Rating of sheet weight Run No. 1,000X (Percent) (percent) (cc.) cylinder (mm.) (m./min.) to dryer formation (U) (g./m.

5 000 5 1.40 510 s 41.3 Small Poor(2.1) 16.0 5:000 10 1.01 480 14 40.9 do Good 1.25 16.0 6,000 20 0.65 510 20 43.6 do Excellent (0.75)- 16.0 ,000 30 0.67 490 20 41. 16.0 5, 000 0. 65 490 20 16. 0 a, 000 20 1.88 525 15 16. 0 2, 500 20 2. 520 12 16.0

EXAMPLE 2 50 TABLE 3 A commercial NUKP (comferous unbleached kraft pulp) was charged in a TAPPI-Standard Niagara beater, Run number and heated at a consistency of 3% for 3 hours to a Item 1 2 3 Canadian freeness of 300 cc. Then, each of the dyestuffs NBKP=10O% listed in Table 2 was separately added to the stock in an Canadianfreeness =690 cc. amount of 1.0 to 5.0% on the basis of dry fiber, and Conditions in common gfi fij f agent thoroughly mixed with stirring. After being added with n 1 u r i1 umsu1rate=0.e7%. a polyacrylamide (molecular weight, 5,000,000; degree p of hydrolysis, 20%), which had been diluted to a con- Amount of NTA-2Neiliafdieddgngles per 0 1 O 2 0 centration of 0.1%, or with a polyethylene oxide, which i gggi ggg gg gp a e also had been diluted to a concentration of 0.1%, each iightltrgnsmitiitauce (percent)- 93.1: 12.3 41.3 in an amount of 0.01% on the basis of dry fiber, each g gg g tg 3% 3,9 "2 stock were made into handmade sheets by means of a uare-t e sheet machine. The final sheets were comsq yp EXAMPLE 4 pared for the flocculation of colored fibers, and the results obtained were as shown in Table 2.

To the stock treated in a heater in the manner similar to that in Example 3, 1.0% on the basis of dry fiber of a rosin sizing agent and 0.9% on the basis of dry fiber of aluminum sulfate were added to fix the rosin sizing agent at pH 4.5, and then the stock was diluted to a consistency of 0.1%. Each definite quantity of said diluted stock was added with, as a sequestering agent for aluminum ion, 1 to 2 moles of sodium suifosalicylate (SSA-Na) per mole of aluminum sulfate used for fixing the rosin sizing agent. The dispersion degree of fibers was evaluated by measuring the light transmittance with a photoelectric colorimeter. On the other hand, the results of visual inspection were also given in the table, wherein poor" means distinct occurrence of flocculation on adding the Run number Conditions in common NBKP=100% Canadian ireeness=690 cc.

Amount of rosin sizing agent added=1.0% Aluminum sulfate-=0.9%

Amount of low molecular weight polyacrylamide added (moles per mole of aluminum sulfate added) 0 2 3 Dispersion level:

Light transmittance (percent) 62. 5 73. 5 62. 2 41.1 40. 5 40. 5 Visual inspection Poor Poor Good Good Good Stiiekigt sizing degree (see) 7. 7 7. 7 15. 0 15. 9 18. 5 18. 8

1 Fairly good.

Nora-Run No. l in the table is the case where both low molecular weight polyaerylamide and synthetic mucilaginous material are absent. Run N o. 2 in the table is the case wherein a synthetic mucilaginoius material alone was added without adding a low molecular weight polyacrylamide.

synthetic mucilaginous material, and good means no such flocculation.

EXAMPLE 6 The same stock as that in Example 3 was added with TABLE 4 1.0% of a rosin sizing agent and 0.9% of aluminum Run number r sulfate, and thoroughly mixed with stirring to fix the Item 1 2 3 rosin sizing agent while maintaining pH at 4.5. Then a BKP=100% low molecular weight polyacrylamide having a molecular pH=4.li weight of 700,000 was added in an amount of 2 to 10 Cmdltmnsm canadmnfieenesssgocc' moles per mole of l i u lf dd f fi i Rosin sizing agent=l.0% Aluminum suliate=0.9%

Amount of SSA-Na added (moles ber mole and diluted to a consistency of 0.1%. Each portion of definite quantity of the diluted stock was admixed with r aluminum sulfate added) 0 1.0 2.0 1% on the basis of dry fiber of a high molecular weight fig figgggi (percent) 930 4L5 4L0 polyacrylarnidehaving a molecular Weight of 9,000,000 t gsrgaiiinspegtionuzmju P301 ap g; and a hydrolysis degree of 20%, and made into sheet In S g S Z agree the manner similar to that in Example 5 in order to evalu- The Sttickigt sizing degree in Tables 3 and 4 was determined on a specimen of paper made on a TAPPI- Standard sheet machine.

Item

Conditions in common Run number NB KP 100% Canadian freeness=690 cc.

Amount of rosin sizing agent added=l.0% Aluminum suliate=0.9%

Amount of low molecular weight polacrylamide added (moles per mole of aluminum sulfate added)- 0 0 2 3 6 10 Dispersion level:

Light transmittance (percent) 62.6 73. 5 46.4 40. 0 39. 5 40. 0 Visual inspection Poor Poor Good Good Good Good Stilckigt sizing degree (sec.) 7. 7 7. 7 13. 6 18. 8 23.3 25. 5

NorE.-Run No. 1 in the table is the case where both low molecular weight polyaerylamide and synthetic mucilaginous material are absent. Run No. 2 in the table is the case wherein a synthetic mucilaginous material alone was added without adding a low molecular weight polyacrylamide.

EXAMPLE 5 To the stock treated in a beater in the manner similar to that in Example 3, 1.0% on the basis of dry fiber of a commercial rosin sizing agent and 0.9% on the basis of dry fiber of aluminum sulfate were added, and thoroughly mixed with stirring while maintaining pH at 4.5 to fix the rosin sizing agent.

Subsequently, as shown in Table 5, a low molecular weight polyacrylamide having a molecular Weight of 200,000 was added to each portion of the stock in an amount of '2 to 10 moles per mole of aluminum sulfate added to fix the rosin sizing agent, and each portion of the stock was diluted to 0.1% consistency. To the stock was added 2% on the basis of dry fiber of a synthetic mucilaginous material having a molecular weight of 5,000,000 and a hydrolysis degree of 20%. After elapse of a definite time, the turbidity of the stock suspension was measured with a photoelectric colorimeter in knowing the dispersion level of fibers. On the other hand, the results of visual inspection were also given in the table, wherein poor" means distinct occurrence of flocculation of fibers on adding a polyacrylamide having a molecular weight of 5,000,000 and a hydrolysis degree of 20%, and

EXAMPLE 7 In a Hollander beater 40 kg. of a commercial NBKP was beaten at a consistency of 3% for one hour to a Canadian freeness of 670 cc. to obtain a stock.

To the stock were added 1% on the basis of dry fiber of a commercial rosin sizing agent and L0 to 2.6% on the basis of dry fiber of aluminum sulfate were added, and thoroughly mixed to fix the rosin. The pH of the stock was 4.4 to 4.8. Each rosin sized stock was diluted to 0.1% consistency, and sent to the vat of a cylinder machine, where a low molecular weight polymer of the acrylamide type composed of 95% of acrylamide and 5% of sodium acrylate and having a molecular weight of 200,000, or the one composed of of acrylamide, 10% of acrylonitrile and 10% of sodium acrylate and having a molecular weight of 700,000 was added thereto in order to sequester the aluminum ion. Then, to each stock was added as a synthetic mucilaginous material an aqueous solution of a high molecular weight polyacrylamide having a molecular weight of 5,000,000 and a hydrolysis degree of 20% (abbreviated as PAA-a), or of a high molecular weight polyacrylamide having a molecular weight of 9,000,000 and a hydrolysis degree 3. A process according to claim 2, wherein said chelatof 20% (abbreviated as PAA-b), both solutions having ing agent is disodium ethylenediaminetetraacetate, disobeen previously prepared by dilution to a concentration dium nitrilotriacetate, citric acid, tartaric acid or sodium of 0.1%. From each stock tissue papers were prepared. sulfosalicylate.

One each final paper thus prepared, the test for water 4. A process according to claim 1, wherein said wet absorption degree (period of immersion, min.) was web is admixed with said acrylamide-based anionic polymade to obtain the results as shown in Table 7. The mer which is polyacrylamide in an amount of 1 to 10 machine used was a cylinder Yankee machine of the moles per mole of aluminum sulfate.

uniflow type, and the width of sheet-forming was 445 m 5. A process according to claim 1, wherein said wet mm. web is admixed with an acrylamide-based anionic poly- TABLE 7 Run number Item 1 2 3 4 6 6 7 Amount oisizlng agent added (percent) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Auminumsuliateadded (percent) 2.6 1.0 1.0 1.0 1.0 1.0 1.0 pHinthestoek 4.4 4.6 4.6 4.6 4.6 4.6 4.6 Polymerization degree of low molecular weight W polymer of aerylarnide type 200, 000 700, 000 Amount of the above polymer added (moles per mole of aluminum sulfate) 0 2.0 3.0 5.0 2.0 3.0 15.0

Kind of synthetic mueilaginous material PEO PAA-a PAA-b e Amount of the above agent added (pereent) 0.62 1.4 0.7 Head dlfierence between inside and outside 01 the cylinder (mm.) 22 25 25 25 24 24 M Basiswelght (g./1n. 18.2 12.2 12.8 12.3 12.3 12.5 12.8 Water absorption degree (mm.) 6 2 2 2 3 2 2 What is claimed is: mer which is a copolymer composed of acrylamide and 1. In a process for the preparation of cellulosic paper less than 50% by weight based on total weight of monsheets having a high degree of uniformity through the omers of at least one member selected from the group steps of consisting of acrylic acid salts, methacrylic acid salts,

(a) forming a cellulosic fiber suspension in a vat, said acrylic acid esters, methacrylic acid esters, acrylonitrile,

cellulosic fiber stock having been sized with a rosin and vinyl acetate, in an amount of 1 to 10 moles per sizing agent and aluminum sulfate; mole of aluminum sulfate.

(b) subjecting said suspension to suction at the sur 6. A process according to claim 5 wherein the acrylic face of said vat through a wire mesh, whereby a and methacrylic acid salts are members selected from wet web of said cellulosic fiber is formed; and the group consisting of the sodium, potassium and am- (c) preparing a finished sheet of paper from said wet 4 monium salts and the acrylic and methacrylic acid esters web are members selected from the group consisting of the the improvement which comprises (1) sequestering the methyl, ethyl, n-propyl and n-butyl esters. excess aluminum ion by the addition of a sequestering amount of a member selected from the group consisting References C t of (i) a chelating agent and (ii) an acrylamide-based UNITED STATES PATENTS anionic polymer having a molecular weight of less than 1,000,000; and (2) after sequestering the excess free 3,076,740 1963 Reynolds et 1 8X aluminum ion, the inclusion in said fiber suspension of 3,019,157 11/ 1962 Reynolds et a1. 152-180X an effective amount of a synthetic mucilaginous material 3,391,057 7/ 1968 Spence et 8 X to provide for the formation of paper sheets of an even ,6 3/ '69 r ico et a1. 162180X texture and quality by obviating the problem of cellulose ,1 ,2 2 11/1963 Jones l62--180X fiber slippage on said wire mesh and providing a uniform 3,332,834 7/ 1967. Reynolds 1 8 X dispersion of the fibers in the vat, said synthetic mucil- 3,2 5,0 2 6/ 1966 Sheetz 162-168 aginous material being a polyacrylamide of a molecular weight of more than 3,000,000 and a hydrolysis degree ROBERT LINDSAY, Pnmary Exammer of 10 to 30%, and said effective amount being from 0.01 FREI, Assistant Examiner to 2% based on the weight of the dry fiber.

2. A process according to claim 1, wherein said wet US. Cl. X.R. web is admixed with said chelating agent in an amount 162-158, 180, 183 of 0.05 to 2 moles per mole of aluminum sulfate. 

